Small refactor and util for OptLevel

[tcoratger]

• Small refactor
• Implementation of (in order to reduce duplicated code):
  • From<usize> for OptLevel
  • Into<usize> for OptLevel
  • From<u8> for OptLevel

Checklist

• Linked to Github Issue
• Unit tests added
• Integration tests added.
• This change requires new documentation.
  • Documentation has been added/updated.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 44.82759% with 16 lines in your changes are missing coverage. Please review.

Project coverage is 89.74%. Comparing base (9a3e2ed) to head (a93b64b).
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/ffi.rs	42.85%	12 Missing ⚠️
src/bin/cairo-native-run.rs	0.00%	2 Missing ⚠️
src/bin/cairo-native-compile.rs	0.00%	1 Missing ⚠️
src/bin/cairo-native-test.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #570   +/-   ##
=======================================
  Coverage   89.73%   89.74%           
=======================================
  Files         108      108           
  Lines       34532    34528    -4     
=======================================
- Hits        30989    30987    -2     
+ Misses       3543     3541    -2     

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